code: def test_sign(backend_default):
      inputs = np.array([-1, -0.5, 0, 0.5, 1]).reshape((5, 1))
      outputs = np.array([-1, -1, 1, 1, 1]).reshape((5, 1))
      compare_tensors(Sign(), inputs, outputs, tol=0)
  
imports: from math import tanh
  import numpy
  from neon import NervanaObject
  from neon.transforms import Identity, Rectlin, Softmax, Tanh, Logistic, Sign, PixelwiseSoftmax
  from utils import allclose_with_out
label_desc: Use image node_id 25 for calling a global function with example usage: test_sign(backend_default) without return types